The present invention relates to an interference measurement apparatus and a probe used for an interference measurement apparatus, more particularly, to an interference measurement apparatus and a probe used for an interference measurement apparatus which utilize a phase modulation method.
FIG. 11 shows a constitutional view of a conventional interference measurement apparatus (see the Publication of Unexamined Japanese Patent Application No. 64-88202).
This interference measurement apparatus comprises a light source instrument 111, a half mirror 113, a movement corner cube 114, a reference corner cube 115, a polarization beam splitter 116, detectors 117 and 118, and a signal processing circuit.
In such interference measurement apparatus, a luminous flux P emitted from the light source instrument 111 is divided into the measurement luminous fluxes P1 and P2 by the half mirror 113 as the beam splitter. The measurement luminous flux P1 is reflected by the movement corner cube 114 serving as a reflection means disposed at a measurement position on the measurement optical path. The reference light P2 is reflected by the reference corner cube 115 disposed on the reference optical path. The interference light P3 of both luminous fluxes is guided to the polarization beam splitter 116 and is separated into the P and S components by the polarization beam splitter 116. The interference light of the P component is guided to the detector 117, and the interference light of the S component is guided to the detector 118. In accordance with the interference state based on the movement of the movement corner cube 114, the interference signals Q1 and Q2 shifted by 90.degree. from each other are inputted to the signal processing circuit from the detectors 117 and 118, and subjected to a predetermined signal processing by the signal processing circuit, so that the distance to the movement corner cube 114 is measured.
Next, a second background known art will be described.
FIG. 12 shows a conventional bulk type phase modulation interference measurement apparatus (see the Publication of Unexamined Japanese Patent Application No. 64-12205).
In this apparatus, the coherent light P emitted from a laser light source 121 is split into a reference light P1 and a measurement light P2, and the reference light P1 is reflected by a reference prism 123. The measurement light P2 is reflected by a measurement prism 124, and the returned reference light P1 and the returned measurement light P2 are allowed to interfere with each other and the interfered light is guided to a photodetector 125. Here, a measurement prism 124 is moved to the arrow direction or to opposite direction to the arrow, and the reference prism 123 is vibrated with a predetermined period as shown by the arrow. The difference of the optical distance of the reference light P1 from that of the measurement light P2 is relatively changed with the predetermined period, and the interference signal based on the interference light which changes in response to the change of that difference is obtained by the photodetector 125. In the manner described above, the direction of the phase change of the measurement light (movement direction of the measurement prism 124) can be obtained, the movement amount of the measurement prism 124 can be obtained without an influence of the DC bias component based on the light amount or the like.
However, in the first conventional background art, the structure of the optical system is complicated. In the second conventional background art, a driving section for mechanically driving the reference prism is necessary, so, the structure of the control system is complicated. Moreover, in the first and second conventional background arts, since the prism is used as the reflection mirror, the range of use is limited by the size of the prism itself and an axial shift may occur, and it is hard to handle it.